Tantalum oxide film, use thereof, process for forming the same and composition

ABSTRACT

A composition for forming a high-quality tantalum film which is advantageously used as an capacitor insulating film and a process for forming the high-quality tantalum film. The composition for forming a tantalum oxide film, which comprises at least one tantalum compound selected from the group consisting of a reaction product of a compound capable of reacting with a tantalum alkoxide and a tantalum alkoxide and a hydrolyzate of the reaction product, and a solvent, and the process for forming the tantalum oxide film by applying this composition to a substrate and heating it.

FIELD OF THE INVENTION

The present invention relates to a composition for forming a tantalumoxide film, a process for forming a tantalum oxide film, a tantalumoxide film and use thereof. More specifically, it relates to acomposition for forming a tantalum oxide film suitable for use as aninsulating film for semiconductor devices, such as a capacitorinsulating film or a gate insulating film for use in DRAMs, a tantalumoxide film, a process for forming the same and use of a tantalum oxidefilm as an insulating film.

PRIOR ART

The area of a capacitor in a DRAM (Dynamic Random Access Memory) hasbeen becoming smaller due to increases in the integration and density ofa semiconductor device. When the capacity becomes smaller as the area ofa capacitor decreases, the erroneous operation of a device may occur dueto a software error or the like. Therefore, even when the area of thecapacitor decreases, a sufficient capacity must be ensured. One of themeans of solving this problem is to use an insulating film having a highdielectric constant (high dielectric film) as a capacitor insulatingfilm. A SiO₂ or Si₃N₄ film has been used as a capacitor insulating filmand capacity has been ensured by a 3-D memory cell structure. However,due to a recent tendency to rapidly increase the integration and reducethe design rule of a DRAM, it is becoming difficult to ensure thecapacity of a memory cell with prior art methods.

Tantalum oxide is characterized in that it has a dielectric constant 3times or more higher than SiO₂ and Si₃N₄ which have been used incapacitor insulating films and a thin film thereof having excellent stepcoverage can be easily deposited by CVD. Therefore, researches intotantalum oxide as the next-generation DRAM capacitor insulating film arenow under way.

The method of forming a tantalum oxide insulating film by CVD isdisclosed in Applied Physics 69(9), p. 1067 (2000). Various studies ontantalum materials used for CVD are reported in Electronic Materials,No. 7, p. 18 (2000).

However, tantalum oxide insulating films formed by these prior artmethods contain large quantities of impurities and oxygen defect due totheir raw materials and film forming methods, which causes a leakcurrent and reduces dielectric breakdown. A tantalum alkoxide used as araw material to form a film by CVD has problems that its hydrolyzabilityis high and that impurities such as carbon remain in the film in largequantities.

Further, film formation by CVD requires a bulky apparatus which isexpensive itself and consumes a large amount of energy for vacuum andplasma systems, thereby boosting product costs.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide atantalum-containing composition for forming a high-quality tantalumoxide film easily and effectively, which solves the above problems, anda process for producing the composition.

It is another object of the present invention to provide a high-qualitytantalum oxide film and a process for forming the same.

It is still another object of the present invention to provide use of atantalum oxide film.

Other objects and advantages of the present invention will becomeapparent from the following description.

MEANS FOR SOLVING THE PROBLEM

According to the present invention, firstly, the above objects andadvantages of the present invention are attained by a composition forforming a tantalum oxide film, comprising at least onetantalum-containing product selected from the group consisting of (A1) areaction product of (a1) a tantalum alkoxide and (a2) at least onecompound selected from the group consisting of an amino alcohol,compound having two or more hydroxyl groups in the molecule (excludingamino alcohols), β-diketone, β-ketoester, ester of β-dicarboxylic acid,lactic acid, ethyl lactate and 1,5-cyclooctadiene and (A2) a hydrolyzateof the reaction product.

According to the present invention, secondly, the above objects andadvantages of the present invention are attained by a process forforming a tantalum oxide film, comprising applying the above compositionto the surface of a substrate and subjecting it to a heat treatmentand/or an optical treatment.

Thirdly, the above objects and advantages of the present invention areattained by a tantalum oxide film formed by the above process.

Fourthly, the above objects and advantages of the present invention areattained by an insulating film for semiconductor devices, which has atantalum oxide film formed by the above process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an NMR spectrum diagram of a product obtained in SyntheticExample 1;

FIG. 2 is an ¹H-NMR spectrum diagram of a tantalum-containing productobtained in Synthetic Example 2;

FIG. 3 is an ¹H-NMR spectrum diagram of a product obtained in SyntheticExample 7;

FIG. 4 is an ¹H-NMR spectrum diagram of a white solid obtained inSynthetic Example 10;

FIG. 5 is an ESCA spectrum diagram of a Ta₂O₅ film obtained in Example1;

FIG. 6 is an ESCA spectrum diagram of a tantalum oxide film obtained inExample 4:

FIG. 7 is an ESCA spectrum diagram of a tantalum oxide film obtained inExample 9: and

FIG. 8 is an ESCA spectrum diagram of a tantalum oxide film obtained inExample 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Component (a1)

The tantalum alkoxide (a1) used in the present invention is preferably acompound represented by the following formula (1):

Ta(OR)₅  (1)

wherein R is an alkyl group having 1 to 6 carbon atoms and five R's maybe the same or different.

Illustrative examples of the tantalum alkoxide include tantalumpentamethoxide, tantalum pentaethoxide, tantalum pentaisopropoxide andtantalum pentabutoxide. Out of these, tantalum pentaethoxide, tantalumpentaisopropoxide and tantalum pentabutoxide are preferred. Thesetantalum alkoxides may be used alone or in combination of two or more.

Component (a2)

The component (a2) used in the present invention is at least onecompound selected from the group consisting of an amino alcohol,compound having two or more hydroxyl group in the molecule (excludingamino alcohols), β-diketone, β-ketoester, ester of β-dicarboxylic acid,lactic acid, ethyl lactate and 1,5-cyclooctadiene.

Examples of the compound having two or more hydroxyl groups in themolecule (excluding amino alcohols) include alcohols having two or morehydroxyl groups in the molecule (excluding amino alcohols) and phenolshaving two or more hydroxyl groups in the molecule.

Out of the above compounds, amino alcohols, alcohols having two or morehydroxyl groups in the molecule (excluding amino alcohols) and phenolshaving two or more hydroxyl groups in the molecule are preferred, andamino alcohols and alcohols having two or more hydroxyl groups in themolecule (excluding amino alcohols) are more preferred.

The above amino alcohols include triethanolamine, diethanolamine,triisopropanolamine, diisopropanolamine, methyldiethanolamine andethydiethanolamine. Out of these, triethanolamine and diethanolamine areparticularly preferred.

Examples of the alcohols having two or more hydroxyl groups in themolecule (excluding amino alcohols) include dialcohols such as ethyleneglycol, propylene glycol, butanediol, pentanediol, hexanediol,heptanediol, octanediol, nonanediol, decanediol, diethylene glycol,bistrimethylene glycol, glycerol monomethyl ether, glycerol monoethylether and hydroquinone; and polyhydric alcohols such as glycerol. Out ofthese, diethylene glycol, butanediol and pentanediol are particularlypreferred.

Examples of the phenols having two or more hydroxyl groups in themolecule include polyhydric phenols such as catechol, resorcin,hydroquinone and phloroglucin. Out of these, hydroquinone isparticularly preferred.

Examples of the above β-diketone include acetylacetone,propionylacetone, methyl diacetylmethane, dipropionylmethane,n-butyrylacetone, isobutyrylacetone, 3-methyl-2,4-hexanedione,diacetylethylmethane, n-valerylacetone, propionyl-n-butyrylmethane,3-methyl-2,4-hexanedione, diacetylethylmethane, n-valerylacetone,propionyl-n-butyrylmethane, 3-methyl-2,4-heptanedione,isovalerylacetone, pivaloylacetone, isopropyldiacetylmethane,caproylacetone, di-n-butyrylmethane,2,2,6,6-tetramethyl-3,5-heptanedione, benzoylacetone,3-phenyl-2,4-pentanedione, dibenzoylmethane,ethoxycarbonyldiacetylmethane and1,1,1,5,5,5-hexafluoro-2,4-pentanedione. Out of these, acetylacetone andpropionylacetone are particularly preferred.

Examples of the above β-ketoester include methyl acetoacetate, ethylacetoacetate and methyl-α-methyl acetoacetate. Out of these, methylacetoacetate and ethyl acetoacetate are particularly preferred.

Examples of the above β-dicarboxylate include dimethyl malonate, diethylmalonate, dibutyl malonate, dihexyl malonate, dioctyl malonate,diundecyl malonate, dihexadecyl malonate, di-9-octadecyl malonate,di-9,12-octadecadienyl malonate and di-9,11,13-octadecatrienyl malonate.Out of these, dimethyl malonate and diethyl malonate are particularlypreferred.

The above compounds may be used alone or in combination of two or more.

The reaction between the tantalum alkoxide (a1) and the component (a2)is carried out by using the component (a2) in an amount of preferably0.1 to 1,000 mols, more preferably 0.5 to 100 mols, particularlypreferably 1 to 10 mols based on 1 mol of the tantalum alkoxide (a1).

The reaction temperature may be preferably −30 to 150° C., morepreferably 0 to 100° C., particularly preferably 0 to 70° C. Thereaction pressure is normal pressure, optionally under increasedpressure or reduced pressure.

The reaction between the tantalum alkoxide (a1) and the component (a2)may be carried out in the presence of a monoalcohol (excluding aminoalcohols) and/or a monophenol.

Illustrative examples of the monoalcohol (excluding amino alcohols)include methanol, ethanol, propanol, isopropanol, butanol, tert-butanol,hexanol, cyclohexanol, octanol, ethylene glycol monomethyl ether,ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,propylene glycol monomethyl ether, propylene glycol monoethyl ether,glycerol dimethyl ether and glycerol diethyl ether.

Illustrative examples of the monophenol include phenol, methyl phenol,dimethyl phenol, trimethyl phenol, ethyl phenol, diethyl phenol andtriethyl phenol.

Out of these, phenol, methyl phenol and ethyl phenol are preferred.

When the reaction between the tantalum alkoxide (a1) and the component(a2) is carried out in the presence of a monoalcohol (excluding aminoalcohols) and/or a monophenol, the total amount of the monoalcoholand/or the monophenol is preferably 10 mols or less, more preferably 5mols or less, particularly preferably 3 mols or less based on 1 mol ofthe component (a2). When the amount is larger than 10 mols, the reactionbetween the tantalum alkoxide (a1) and the component (a2) may beimpeded.

The above reaction may be carried out in the presence of a solvent asrequired. When a solvent is used, a solvent which does not react withthe tantalum alkoxide (a1), the component (a2) and the reaction productthereof is preferably used.

Illustrative examples of the solvent include hydrocarbon-based solventssuch as n-pentane, cyclopentane, n-hexane, cyclohexane, n-heptane,cycloheptane, n-octane, cyclooctane, decane, cyclodecane,dicyclopentadiene hydride, benzene, toluene, xylene, durene, indene,tetrahydronaphthalene, decahydronaphthalene and squalane; ether-basedsolvents such as diethyl ether, dipropyl ether, dibutyl ether, ethyleneglycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycolmethyl ethyl ether, diethylene glycol diethyl ether, diethylene glycolmethyl ethyl ether, tetrahydrofuran, tetrahydropyran,1,2-dimethoxyethane, bis(2-methoxyethyl)ether and p-dioxane; and polarsolvents such as propylene carbonate, γ-butyrolactone,N-methyl-2-pyrrolidone, dimethyl formamide, acetonitrile, dimethylsulfoxide, methylene chloride and chloroform.

Out of these, diethyl ether, dipropyl ether, dibutyl ether,tetrahydrofuran, dimethyl formamide, acetonitrile, dimethyl sulfoxide,methylene chloride and chloroform are particularly preferred.

These solvents may be used alone or in combination of two or more.

When the reaction between the tantalum alkoxide (a1) and the component(a2) is carried out in the presence of a solvent, the amount of thesolvent is preferably 1 to 100 ml, more preferably 5 to 50 ml,particularly preferably 5 to 30 ml based on 1 g of the tantalum alkoxide(a1).

The above reaction product is assumed to be the following substance, forexample:

i) a reaction product in which some or all of the alkoxyl groups of thetantalum alkoxide are eliminated, at least one hydroxyl group in thecomponent (a2) loses its hydrogen atom, and the oxygen atom contained inthe hydroxyl group losing its hydrogen atom is bonded to a tantalum atomwhen the component (a2) contains an amino alcohol, an alcohol having twoor more hydroxyl groups in the molecule, a phenol having two or morehydroxyl groups in the molecule, lactic acid or ethyl lactate. When aplurality of hydroxyl groups in one molecule of the component (a2) takepart in the reaction, tantalum atoms bonded to the hydroxyl groups maybe the same or different.

ii) a reaction product in which some or all of the alkoxyl groups of thetantalum alkoxide are eliminated, a CH₂ group sandwiched between twocarbonyl groups in the component (a2) loses its hydrogen atoms, theβ-diketone structure losing the hydrogen atoms takes a resonancestructure, and a chelate bond is formed at one tantalum atom when thecomponent (a2) contains a β-diketone, β-ketoester or ester ofβ-dicarboxylic acid.

iii) a reaction product in which some or all of the alkoxyl groups ofthe tantalum alkoxide are eliminated, at least one carboxyl group in thecomponent (a2) loses its hydrogen atom, and an oxygen atom contained inthe carboxyl group losing its hydrogen atom is bonded to a tantalum atomwhen the component (a2) contains lactic acid. The carboxyl group losingits hydrogen atom may take a resonance structure and be chelate-bondedto one tantalum atom.

iv) a reaction product in which the two oxygen atoms of an ester groupare bonded to a tantalum atom when the component (a2) contains ethyllactate.

v) a reaction product in which an oxygen atom or nitrogen atom containedin the component (a2) and bonded to a tantalum atom is further bonded toa tantalum atom contained in another reaction product or an unreactedtantalum alkoxide in i) to iv).

vi) a composition in which some or all of the alkoxyl groups of thetantalum alkoxide are eliminated and at least one double bond containedin 1,5-cyclooctadiene is coordinately bonded to at least one tantalumatom when the component (a2) contains 1,5-cyclooctadiene.

vii) a reaction product in which an oxygen atom or nitrogen atomcontained in the component (a2) or an unreacted product of a monoalcoholor monophenol optionally added is bonded to a tantalum atom contained inany one of the reaction products i) to vi).

viii) a reaction product in which a tantalum atom contained in any oneof the reaction products i) to vii) is bonded to a tantalum atomcontained in another reaction product or an unreacted tantalum alkoxidethrough an oxygen atom.

ix) a reaction product in which a tantalum atom contained in any one ofthe reaction products i) to viii) is crosslinked with a tantalum atomcontained in another reaction product or a tantalum atom contained in anunreacted tantalum alkoxide through the oxygen atom of an alkoxyl groupremaining in the reaction product or an alkoxyl group contained in theunreacted tantalum alkoxide.

x) a mixture of two or more of the above reaction products.

The newly formed bond may be, for example, a covalent bond, ionic bond,coordinate bond, hydrogen bond or intermediate bond therebetween.

The above reaction products may contain an unreacted alkoxyl group or analkoxyl group obtained by an exchange reaction between an alkoxyl groupcontained in the tantalum alkoxide and a monoalcohol optionally added.

The above reaction products may contain an unreacted alkoxyl group or analkoxyl group obtained by an exchange reaction between an alkoxyl groupcontained in the tantalum alkoxide and a monoalcohol optionally added(therefore, these may be generally referred to as “unreacted alkoxylgroup” hereinafter).

The reaction product used as the component [A] in the present inventionhas a reaction conversion defined by the following equation (1) of 50mol % or more, preferably 70 mol %, particularly preferably 85 mol % ormore.

Reaction conversion={1−(total number of unreacted alkoxyl groupscontained in reaction product/total number of alkoxyl groups containedin raw material tantalum alkoxide)}×100 (mol %)  (1)

When this value is smaller than 50 mol %, the electrical properties ofthe formed tantalum oxide film may become unsatisfactory.

The hydrolyzate of the above reaction product can be synthesized byheating the above reaction product at room temperature to 100° C. underagitation in the presence of preferably 0.01 to 1,000 mols of waterbased on 1 equivalent of the tantalum atom.

The hydrolyzate of the above reaction product includes a compoundobtained by hydrolyzing all of the hydrolysable moiety and a partialhydrolyzate in which part of the hydrolysable moiety are hydrolyzed andother part of the moiety remains unhydrolyzed.

In the present invention, the above reaction products and hydrolyzatesthereof may be used alone or in combination of two or more.

[B] Ester of Orthocarboxylic Acid

The composition of the present invention can further comprise [B] anester of orthocarboxylic acid.

The ester of orthocarboxylic acid [B] reacts with water existent inenvironment to reduce the adverse effect of humidity in the atmospherein the step of forming a tantalum oxide film from the composition of thepresent invention, particularly a composition which comprises thereaction product of the component (a1) and the component (a2) as thecomponent (A). Therefore, a tantalum oxide film formed from thecomposition of the present invention containing the ester oforthocarboxylic acid [B] has high quality.

The mechanism that the ester of orthocarboxylic acid [B] reacts withwater is assumed to be represented by the following formula (2):

R¹C(OR²)₃+3H₂O→R¹COOH+3R²OH+H₂O  (2)

wherein R¹ and R² are each an alkyl group or aryl group.

Illustrative examples of the ester of orthocarboxylic acid [B] includetrimethyl orthoformate, triethyl orthoformate, tripropyl orthoformate,tributyl orthoformate, tripentyl orthoformate, diethylpropylorthoformate, triphenyl orthoformate, trimethyl orthoacetate, triethylorthoacetate, tripropyl orthoacetate, tributyl orthoacetate, tripentylorthoacetate, diethylpropyl orthoacetate, triphenyl orthoacetate,trimethyl orthopropionate, triethyl orthopropionate, tripropylorthopropionate, tributyl orthopropionate, tripentyl orthopropionate,diethylpropyl orthopropionate, triphenyl orthopropionate, trimethylorthobutyrate, triethyl orthobutyrate, tripropyl orthobutyrate, tributylorthobutyrate, tripentyl orthobutyrate, diethylpropyl orthobutyrate,triphenyl orthobutyrate, trimethyl ortholaurate, triethyl ortholaurate,tripropyl ortholaurate, tributyl ortholaurate, tripentyl ortholaurate,diethylpropyl ortholaurate, triphenyl ortholaurate, trimethylorthobenzoate, triethyl orthobenzoate, tripropyl orthobenzoate, tributylorthobenzoate, tripentyl orthobenzoate, diethylpropyl orthobenzoate,triphenyl orthobenzoate, trimethyl ortholactate, triethyl ortholactate,tripropyl ortholactate, tributyl ortholactate, tripentyl ortholactate,diethylpropyl ortholactate and triphenyl ortholactate.

Out of these orthocarboxylates, aliphatic esters are preferred from theviewpoint of reactivity with water, and methyl esters and ethyl estersare particularly preferred. Specifically, trimethyl orthoformate,triethyl orthoformate and trimethyl orthobenzoate are particularlypreferred.

These ester of orthocarboxylic acids may be used alone or in combinationof two or more.

The amount of the ester of orthocarboxylic acids [B] in the compositionof the present invention may be suitably determined according to thewater content of the composition and the ambient humidity in the step offorming a tantalum oxide film but preferably 0.05 to 50 wt %, morepreferably 0.1 to 30 wt %, particularly preferably 0.5 to 20 wt % basedon the composition.

The hydroxyl group of a carboxylic acid, alcohol or ortholactate formedby the reaction between water and an ester of orthocarboxylic acid mayreact with a film forming composition, which does not lessen the effectof the present invention.

Composition for Forming a Tantalum Oxide Film

The composition of the present invention is generally used as a solutioncomposition containing the above components dissolved in a solvent.

The solvent which can be used in the present invention is notparticularly limited if it dissolves the above components and does notreact with these. Examples of the solvent include alcohol-based solventssuch as methanol, ethanol, propanol, butanol, hexanol, cyclohexanol,octanol, decanol, ethylene glycol, ethylene glycol monomethyl ether,ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,propylene glycol, propylene glycol monomethyl ether, propylene glycolmonoethyl ether, propylene glycol monopropyl ether, glycerol, glycerolmonomethyl ether, glycerol dimethyl ether, glycerol monoethyl ether andglycerol diethyl ether; and ester-based solvents such as ethylene glycolmonomethyl ether acetate, ethylene glycol monoethyl ether acetate,propylene glycol monomethyl ether acetate, propylene glycol monoethylether acetate, methyl lactate and ethyl lactate in addition to thesolvents which can be used for the reaction between (a1) the tantalumalkoxide and the component (a2).

These solvents may be used alone or in combination of two or more.

Out of these, alcohol-based solvents and mixed solvents of analcohol-based solvent and another polar solvent are preferred from theviewpoints of the solubility of each component and the stability of theobtained composition.

Propylene glycol monomethyl ether, propylene glycol monoethyl ether andpropylene glycol monopropyl ether are preferred as alcohol-basedsolvents. Mixed solvents of an alcohol-based solvent and an ether-basedsolvent and mixed solvents of an alcohol-based solvent and anester-based solvent are preferred as mixed solvents of an alcohol-basedsolvent and another polar solvent.

The mixed solvents of an alcohol-based solvent and an ether-basedsolvent are preferably mixed solvents of at least one alcohol-basedsolvent selected from propylene glycol monomethyl ether, propyleneglycol monoethyl ether and propylene glycol monopropyl ether and atleast one ether-based solvent selected from bis(2-methoxyethyl)ether,diethylene glycol diethyl ether and diethylene glycol methyl ethylether.

The mixed solvents of an alcohol-based solvent and an ester-basedsolvent are preferably mixed solvents of at least one alcohol-basedsolvent selected from propylene glycol monomethyl ether, propyleneglycol monoethyl ether and propylene glycol monopropyl ether and atleast one ester-based solvent selected from propylene glycol monomethylether acetate and propylene glycol monomethyl ether acetate.

Although there are isomers of propylene glycol monoalkyl ethers out ofthese, all of them may be used and mixed solvents thereof may also beused.

When a solvent is used in the step of a reaction between the tantalumalkoxide (a1) and the component (a2), the solvent may be directly usedas a solvent for the composition of the present invention without beingremoved, or removed after the reaction and then newly added after thepurification of the reaction product of the tantalum alkoxide (a1) andthe component (a2) as required. Alternatively, without removing thesolvent used in the reaction step, a similar solvent may be furtheradded to prepare the composition of the present invention.

When the solvent used contains what has a hydroxyl group, it may reactwith the residual alkoxyl group of the reaction product of the tantalumalkoxide (a1) and the component (a2), which does not lessen the effectof the present invention.

When the composition of the present invention contains a solvent, theamount of the solvent may be suitably determined according to thethickness of a desired coating film. However, the total amount ofcomponents other than the solvent in the composition is preferably 50 wt% or less, more preferably 0.5 to 50 wt %, much more preferably 1 to 30wt %, particularly preferably 1 to 20 wt %.

The composition of the present invention may optionally contain atantalum composition other than the above in order to increase thecontent of tantalum in the composition.

A fluorine-based, silicone-based or nonionic-based surface tensionmodifier may be optionally added to the composition of the presentinvention in limits that do not impair the function of interest.

The thus obtained composition may be suitably mixed with fine particlesof a metal oxide such as aluminum oxide, zirconium oxide, titanium oxideor silicon oxide before use.

Process for Forming a Tantalum Oxide Film

A description is subsequently given of the process for forming atantalum oxide film.

The above composition is applied to a substrate to form the coating filmof the composition of the present invention. The surface of thesubstrate may be flat, uneven with a level difference or curved. Theshape of the substrate is not particularly limited and may beblock-like, plate-like or film-like.

The material of the substrate preferably stands the subsequent heattreatment step. Illustrative examples of the material of the substrateinclude glasses, metals, metal compounds, plastics, ceramics andlaminates thereof. The glasses include quartz glass, borosilicate glass,soda glass and lead glass. The metals and metal compounds include gold,silver, copper, nickel, silicon, aluminum, iron, platinum, ruthenium,tungsten, titanium, cobalt, molybdenum, iridium, stainless steel,aluminum alloy, silicide, tantalum nitride, titanium nitride andruthenium oxide. The plastics include polyimides, polyether sulfones,norbornene-based ring opening polymers and hydrides thereof.

The technique for applying the above solution is not particularlylimited and may be carried on by suitable methods such as spin coating,dip coating, flow coating, curtain coating, roll coating, spray coating,bar coating, ink jetting or printing. The solution may be applied onceor a plurality of times. The thickness of the coating film may besuitably determined according to the thickness of a desired tantalumoxide film. For example, the thickness of the coating film is preferably0.001 to 10 μm, more preferably 0.005 to 1 μm. When the compositioncontains a solvent, the thickness of the coating film should beunderstood as the thickness of the coating film after the removal of thesolvent.

The coating step in the present invention is preferably carried out atan ambient humidity (content of water vapor in the atmosphere) of 5 g/m³or less, preferably 3 g/m³. When the humidity is higher than 5 g/m³, itmay exert a bad influence upon the insulating properties of the formedtantalum oxide film.

When the composition of the present invention comprises a predeterminedamount of an ester of orthocarboxylic acid, the above step of forming acoating film can be carried out without being influenced by humidity(content of water vapor in the atmosphere). For example, when the abovestep is carried out at an ambient humidity of more than 5 g/m³, ahigh-quality tantalum oxide film can be obtained and when the above stepis carried out at an ambient humidity of 7 g/m³ or more, particularly 9g/m³ or more, a high-quality tantalum oxide film can be obtained.

The thus formed coating film is then converted into a tantalum oxidefilm by a heat and/or optical treatment.

The heat treatment temperature is preferably 200° C. or more, morepreferably 300 to 900° C., much more preferably 350 to 800° C. Althoughthe heating time may be suitably determined according to the thicknessof a coating film, in order to obtain a high-quality film, it ispreferably 5 minutes or more, more preferably 15 to 90 minutes, muchmore preferably 30 to 60 minutes.

As for the atmosphere for the heating step, a higher content of oxygenis more preferred.

As the atmosphere for the above heat treatment may be used, for example,air, pure oxygen, ozone, N₂O, a mixture thereof, or a mixed gas of anoxidized gas thereof and an inert gas such as nitrogen, helium or argon.

The light source used for the above photo-treatment is a low-pressure orhigh-pressure mercury lamp, deuterium lamp, discharge light of a raregas such as argon, krypton or xenon, YAG laser, argon laser, carbonicacid gas laser or exima laser such as XeF, XeCl, XeBr, KrF, KrCl, ArF orArCl. The output of the above light source is preferably 10 to 5,000 W,more preferably 100 to 1,000 W. The irradiation time is preferably 0.1to 60 minutes, more preferably 1 to 30 minutes. The wavelength of thelight source is not particularly limited but preferably includes awavelength of 170 to 600 nm.

The atmosphere for the optical treatment may be the same as that for theabove heat treatment. The temperature of the photo-treatment is notparticularly limited but generally room temperature to 500° C. Thecoating film may be exposed through a mask so that only a specificportion can be exposed.

To obtain a higher quality tantalum oxide film, it is preferred that theabove heat treatment and optical treatment should be both carried out.The order of these treatments may be arbitrary and both may be carriedout at the same time. The obtained tantalum film can be made amorphousor crystalline according to the conditions of the heat treatment and/oroptical treatment.

Optionally, the tantalum oxide film formed as described above may befurther subjected to an oxygen plasma or UV-ozone treatment before use.

The thus obtained tantalum oxide film has a dielectric constant of 15 to25 in an amorphous state and 25 to 60 in a crystalline state and a smallleak current and can be advantageously used as a high dielectric filmsuch as an insulating film for semiconductor devices, for example, acapacitor insulating film or gate insulating film for use in DRAMs, aswell as anti-reflection film, passivation film or barrier film.

The tantalum oxide film for use as an insulating film for semiconductordevices has a leak current of preferably 10⁻²A/cm² or less, morepreferably 10⁻⁴ A/cm² or less.

EXAMPLES

The following examples are provided for the purpose of furtherillustrating the present invention but are in no way to be taken aslimiting.

Synthetic Example 1

A mixed solution of 10 g of triethanolamine and 67 ml of tetrahydrofuran(THF) was added to a solution of 8.1 g of tantalum pentaethoxidedissolved in 67 ml of THF in a nitrogen atmosphere under agitation atroom temperature in 15 minutes. After the end of addition, they werefurther stirred at room temperature for 1 hour. The reaction solutionturned slightly cloudy from achromatic and transparent. Thereafter, itwas concentrated under reduced pressure and the residue was washed withhexane, re-dissolved in a small amount of tetrahydrofuran andre-precipitated with hexane. The obtained white solid was separated byfiltration and dried under reduced pressure. When it was analyzed by¹H-NMR, a peak derived from tantalum pentaethoxide disappeared and apeak derived from triethanolamine appeared. The yield was 80%. Thereaction conversion of the ethoxyl groups of the raw material tantalumpentaethoxide was 100 mol %. When the number average molecular weight ofthe reaction product was measured by GPC analysis, it was 1,500.

The GPC measurement was made under the following conditions (the sameshall apply to Synthetic Examples 2 to 5, 7, 8 and 10).

Solvent: tetrahydrofuran (THF)

Concentration: 0.1 g of a tantalum compound dissolved in 10 ml of THF

Standard sample: standard polystyrene of Pressure Chemical Co., Ltd.

Apparatus: high-temperature high-speed gel permeation chromatograph(Model 1500-C ALC/GPC of Waters Co., Ltd.)

Column: SHODEX A-80M of Showa Denko K. K. (length of 50 cm)

Measurement temperature: 40° C.

Flow rate: 1 ml/min

FIG. 1 shows an NMR chart of the product.

Synthetic Example 2

8.12 (20 mmol) of tantalum pentaethoxide and 50 ml of tetrahydrofuran(THF) were fed to a 200 ml eggplant-like flask the inside of which hadbeen fully substituted by nitrogen in a nitrogen atmosphere and 8.1 g(76 mmol) of diethylene glycol was added to the flask under agitation atroom temperature in 15 minutes. Thereafter, they were further stirred atroom temperature for 1 hour.

The reaction solution remained achromatic and transparent but itsviscosity slightly increased.

Thereafter, the solvent was completely removed under reduced pressure toobtain 7.8 g of a white solid (tantalum-containing product).

When it was analyzed by ¹H-NMR, a peak derived from an unreacted ethoxylgroup of tantalum pentaethoxide and a peak derived from a reactionproduct of tantalum pentaethoxide and diethylene glycol were observedand the integral ratio thereof was 1:20. When the reaction conversion ofthe ethoxyl groups of tantalum pentaethoxide was calculated from thisratio, it was 91 mol %.

When the number average molecular weight of the product was measured byGPC analysis, it was 730. When the content of tantalum was calculated byelemental analysis, it was 40.9 wt %.

FIG. 2 shows a ¹H-NMR chart of the product.

Synthetic Example 3

The procedure of Synthetic Example 2 was repeated to produce 12.5 g of awhite solid (tantalum-containing product) except that the amount ofdiethylene glycol was changed to 16.2 g (584 mmol).

When the obtained solid was analyzed by ¹H-NMR, a peak derived from anunreacted ethoxyl group of tantalum pentaethoxide and a peak derivedfrom a reaction product of tantalum pentaethoxide and diethylene glycolwere observed, and the integral ratio thereof was 1:36. When thereaction conversion of the ethoxyl groups of tantalum pentaethoxide wascalculated from this ratio, it was 93 mol %.

When the number average molecular weight of the product was measured byGPC analysis, it was 680. When the content of tantalum was calculated byelemental analysis, it was 25.5 wt %.

Synthetic Example 4

The procedure of Synthesis Example 2 was repeated to produce 4.2 g of awhite solid (tantalum-containing product) except that 2.9 g (50 mmol) ofethylene glycol was used in place of 8.1 g of diethylene glycol. Whenthe obtained solid was analyzed by ¹H-NMR, a peak derived from anunreacted ethoxyl group of tantalum pentaethoxide and a peak derivedfrom a reaction product of tantalum pentaethoxide and ethylene glycolwere observed, and the integral ratio thereof was 1:14. When thereaction conversion of the ethoxyl groups of tantalum pentaethoxide wascalculated from this ratio, it was 91 mol %.

When the product was measured by GPC analysis, its molecular weightdistribution was multi-modal and showed a peak at 500 to 1,540. When thenumber average molecular weight of the product was calculated, it was540. When the content of tantalum was calculated by elemental analysis,it was 54.2 wt %.

Synthetic Example 5

The procedure of Synthetic Example 2 was repeated to produce 8.8 g of awhite solid (tantalum-containing product) except that 5.8 g (10 mmol) ofethylene glycol was used in place of 8.1 g of diethylene glycol. Whenthe obtained solid was analyzed by ¹H-NMR, a peak derived from anunreacted ethoxyl group of tantalum pentaethoxide and a peak derivedfrom a reaction product of tantalum pentaethoxide and ethylene glycolwere observed, and the integral ratio thereof was 1:30. When thereaction conversion of the ethoxyl groups of tantalum pentaethoxide wascalculated from this ratio, it was 96 mol %.

When the product was measured by GPC analysis, its molecular weightdistribution was multi-modal and showed a peak at 500 to 1,200. When thenumber average molecular weight of the product was calculated, it was740. When the content of tantalum was calculated by elemental analysis,it was 39.2 wt %.

Synthetic Example 6

8.12 g (20 mmol) of tantalum pentaethoxide and 50 ml of tetrahydrofuran(THF) were fed to a 200 ml eggplant-like flask the inside of which hadbeen fully substituted by nitrogen in a nitrogen atmosphere, and 5.5 g(50 mmol) of hydroquinone was added to the flask under agitation at roomtemperature in 15 minutes.

A white solid separated out and became cloudy as soon as addition ofhydroquinone was started.

Thereafter, they were further stirred at room temperature for 1 hour.

After the end of the reaction, the formed solid was isolated byfiltration, and the solvent was completely removed under reducedpressure to obtain 8.6 g of a white solid (tantalum-containing product).

When the obtained white solid was analyzed by ¹H-NMR, a peak derivedfrom an unreacted ethoxyl group of tantalum pentaethoxide and a peakderived from a reaction product of tantalum pentaethoxide andhydroquinone were observed, and the integral ratio thereof was 1:21.When the reaction conversion of the ethoxyl groups of tantalumpentaethoxide was calculated from this ratio, it was 94 mol %. When thecontent of tantalum was calculated by elemental analysis, it was 39.8 wt%.

Synthetic Example 7

15 g (37 mmol) of tantalum pentaethoxide and 150 ml of tetrahydrofuran(THF) were fed to a 300 ml eggplant-like flask the inside of which hadbeen fully substituted by nitrogen in a nitrogen atmosphere and cooledto 0° C., and a solution of 9.8 g (92 mmol) of diethylene glycoldissolved in 75 ml of THF was added to the flask under agitation at roomtemperature in 1.5 hours. Thereafter, they were further stirred at 0° C.for 8 hours. The reaction solution remained achromatic and transparentbut its viscosity slightly increased.

The solvent was then completely removed under reduced pressure, and theresidue was washed with 25 ml of hexane and vacuum dried to obtain 13 gof a white solid.

When the obtained white solid was analyzed by ¹H-NMR, a peak derivedfrom an unreacted ethoxyl group of tantalum pentaethoxide and a peakderived from a reaction product of tantalum pentaethoxide and diethyleneglycol were observed, and the integral ratio thereof was 1:16. When thereaction conversion of the ethoxyl groups of tantalum pentaethoxide wascalculated from this ratio, it was 86 mol %. When the number averagemolecular weight of the product was measured by GPC analysis, it was930.

FIG. 3 shows an ¹H-NMR chart of the product.

Synthetic Example 8

A mixed solution of 10 g of triethanolamine and 67 ml of tetrahydrofuran(THF) was added to a solution of 8.1 g of tantalum pentaisopropoxidedissolved in 67 ml of THF in a nitrogen atmosphere under agitation atroom temperature in 15 minutes. After the end of addition, they werefurther stirred at room temperature for 1 hour. The reaction solutionturned slightly cloudy from achromatic and transparent. Thereafter, itwas concentrated under reduced pressure and the residue was washed withhexane, re-dissolved in a small amount of tetrahydrofuran andre-precipitated with hexane. The obtained precipitate was separated byfiltration and dried under reduced pressure. When the product wasanalyzed by ¹H-NMR, a peak derived from an isopropoxyl group of tantalumpentaisopropoxide disappeared and a peak derived from triethanolamineappeared. The yield was 85%. The reaction conversion of the isopropoxylgroups of the raw material tantalum pentaisopropoxide was 100 mol %.When the number average molecular weight of the product was measured byGPC analysis, it was 1,800.

Synthetic Example 9

11 g (20 mmol) of tantalum pentabutoxide and 50 ml of tetrahydrofuran(THF) were fed to a 200 ml eggplant-like flask the inside of which hadbeen fully substituted by nitrogen in a nitrogen atmosphere and 5.5 g(50 mmol) of hydroquinone was added to the flask under agitation at roomtemperature in 15 minutes.

A white solid separated out and became cloudy as soon as addition ofhydroquinone was started.

Thereafter, they were stirred at room temperature for 1 hour.

After the end of the reaction, the formed solid was isolated byfiltration, and the solvent was completely removed under reducedpressure to obtain 12 g of a product.

When the obtained product was analyzed by ¹H-NMR, a peak derived from anunreacted butoxyl group of tantalum pentabutoxide and a peak derivedfrom a reaction product of tantalum pentabutoxide and hydroquinone wereobserved, and the integral ratio thereof was 1:21. When the reactionconversion of the butoxyl groups of tantalum pentabutoxide wascalculated from this ratio, it was 94 mol %.

Synthetic Example 10

8.12 g (20 mmol) of tantalum pentaethoxide and 50 ml of tetrahydrofuran(THF) were fed to a 200 ml eggplant-like flask the inside of which hadbeen fully substituted by nitrogen in a nitrogen atmosphere and 5.3 g(50 mmol) of diethylene glycol was added to the flask under agitation atroom temperature in 15 minutes. Thereafter, they were further stirred atroom temperature for 1 hour. The reaction solution remained achromaticand transparent but its viscosity slightly increased.

Thereafter, the solvent was completely removed under reduced pressure toobtain 7.8 g of a white solid.

When the obtained white solid was analyzed by ¹H-NMR, a peak derivedfrom an unreacted ethoxyl group of tantalum pentaethoxide and a peakderived from a reaction product of tantalum pentaethoxide and diethyleneglycol were observed, and the integral ratio thereof was 1:20. When thereaction conversion of the ethoxyl groups of tantalum pentaethoxide wascalculated from this ratio, it was 88 mol %. When the number averagemolecular weight of the product was measured by GPC analysis, it was870.

FIG. 4 shows an ¹H-NMR chart of the product.

Synthetic Example 11

The procedure of Synthesis Example 6 was repeated to produce 5.3 g of awhite solid except that the amount of hydroquinone was changed to 3.3 g(30 mmol).

When the obtained solid was analyzed by ¹H-NMR, a peak derived from anuntreated ethoxyl group of tantalum pentaethoxide and a peak derivedfrom a reaction product of tantalum pentaethoxide and hydroquinone wereobserved, and the integral ratio thereof was 1:2.4. When the reactionconversion of the ethoxyl groups of pentaethoxide was calculated fromthis ratio, it was 64 mol %.

Example 1

1 g of the tantalum-containing product (tantalum compound) obtained inthe above Synthetic Example 1 was dissolved in 10 ml of a mixed solutionof diethylene glycol monoethyl ether and water (volume ratio of 90/10)to prepare a solution. This solution was filtered with a Teflon(registered trademark) filter having an opening size of 0.2 μm to removeforeign matter and then applied to a silicon substrate by spin coatingat 2,000 rpm. When the coating film was heated at 500° C. for 30 minutesin the presence of air after the solvent was evaporated in the air, atransparent film was obtained on the substrate. The thickness of thisfilm was 800 Å. When the ESCA spectrum of this film was measured, a peakderived from the Ta_(4f7/2) orbit was observed at 26 eV and a peakderived from the O_(1s) orbit was observed at 531 eV, which proved thatthis film was a Ta₂O₅ film. This ESCA spectrum is shown in FIG. 5.

Example 2

A film was formed in the same manner as in Example 1 except that 20 mlof a mixed solution of diethylene glycol monoethyl ether, water and2-propoxyethanol (volume ratio of 80/5/15) was used as a solvent inplace of the mixed solution of diethylene glycol monoethyl ether andwater (volume ratio of 90/10). The thickness of this film was 350 nm.When the ESCA spectrum of this film was measured, a peak derived fromthe Ta_(4f7/2) orbit was observed at 26 eV and a peak derived from theO_(1s) orbit was observed at 531 eV in the same way as Example 1, whichproved that this film was a Ta₂O₅ film.

Example 3

A film was formed in the same manner as in Example 1 except that 10 mlof a mixed solution of diethylene glycol monoethyl ether and2-propoxyethanol (volume ratio of 50/50) was used as a solvent in placeof the mixed solution of diethylene glycol monoethyl ether and water(volume ratio of 90/10). The thickness of this film was 800 nm. When theESCA spectrum of this film was measured, a peak derived from theTa_(4f7/2) orbit was observed at 26 eV and a peak derived from theO_(1s) orbit was observed at 531 eV in the same way as Example 1, whichproved that this film was a Ta₂O₅ film.

Example 4

1 g of the tantalum-containing product obtained in Synthetic Example 2was dissolved in 9 g of diethylene glycol monomethyl ether and theresulting solution was filtered with a Teflon filter having an openingsize of 0.2 μm to prepare a composition for forming a tantalum oxidefilm.

This composition was applied to a silicon substrate having a 0.2μm-thick platinum coating film to a thickness of 0.091 μm by spincoating at 2,000 rpm at an ambient humidity of 2 g/m³. Thereafter, whenthe coating film was heated at 500° C. for 30 minutes in the presence ofair after the solvent was evaporated in the air, a transparent film wasobtained on the substrate. The thickness of this film was 0.030 μm. Whenthe ESCA spectrum of this film was measured, a peak derived from theTa_(4f7/2) orbit was observed at 26 eV and a peak derived from theO_(1s) orbit was observed at 531 eV, which proved that this film was atantalum oxide film. This ESCA spectrum is shown in FIG. 6. Whenplatinum was sputtered on this film to a thickness of 0.060 μm and avoltage of 1.5 V was applied to this film, the leak current was 10⁻⁸A/cm² which was satisfactory as an insulating film for semiconductordevices.

Example 5

A transparent film was obtained in the same manner as in Example 4except that 1 g of the tantalum-containing product obtained in SyntheticExample 3 was used. The thickness of this film was 0.035 μm. When theESCA spectrum of this film was measured, this film was found to be atantalum oxide film. The leak current of the obtained film was 10⁻⁸A/cm² which was satisfactory as an insulating film for semiconductordevices.

Example 6

A transparent film was obtained in the same manner as in Example 4except that 1 g of the tantalum-containing product obtained in SyntheticExample 4 was used. The thickness of this film was 0.032 μm. When theESCA spectrum of this film was measured, this film was found to be atantalum oxide film. The leak current of the obtained film was 10⁻⁸A/cm² which was satisfactory as an insulating film for semiconductordevices.

Example 7

A transparent film was obtained in the same manner as in Example 4except that 1 g of the tantalum-containing product obtained in SyntheticExample 5 was used. The thickness of this film was 0.032 μm. When theESCA spectrum of this film was measured, this film was found to be atantalum oxide film. The leak current of the obtained film was 10⁻⁸A/cm² which was satisfactory as an insulating film for semiconductordevices.

Example 8

A transparent film was obtained in the same manner as in Example 4except that 1 g of the tantalum-containing product obtained in SyntheticExample 6 was used. The thickness of this film was 0.031 μm. When theESCA spectrum of this film was measured, this film was found to be atantalum oxide film. The leak current of the obtained film was 10⁻⁸A/cm² which was satisfactory as an insulating film for semiconductordevices.

Example 9

A composition for forming a tantalum oxide film was prepared bydissolving 1.0 g of the product obtained in Synthetic Example 7 and 0.9g of methyl orthoformate in 8.1 g of 1-methoxy-2-propanol and filteringthe resulting solution with a Teflon (registered trademark) filterhaving an opening size of 0.2 μm.

This composition was then applied to a silicon substrate having a 200nm-thick platinum coating film to a thickness of 100 nm by spin coatingat 2,000 rpm at an ambient humidity of 7 g/m³ and then the solvent wasevaporated at 145° C. The thickness of the film after the removal of thesolvent was 65 nm.

Thereafter, when the film was heated at 400° C. in the air for 30minutes, a transparent film was obtained on the substrate. The thicknessof this film was 40 nm. When the ESCA spectrum of this film wasmeasured, a peak derived from the Ta_(4f7/2) orbit was observed at 26 eVand a peak derived from the O_(1s) orbit was observed at 531 eV, whichproved that this film was a tantalum oxide film. This ESCA spectrum isshown in FIG. 7. When an aluminum film was formed on this film to athickness of 100 nm by deposition and then a voltage of 1.5 V wasapplied, the leak current was 10⁻⁸ A/cm² which was satisfactory as aninsulating film for semiconductor devices.

Example 10

A composition for forming a tantalum oxide film was prepared bydissolving 1.0 g of the product obtained in Synthetic Example 7 and 0.9g of methyl orthoformate in 8.1 g of 1-methoxy-2-propanol and filteringthe resulting solution with a Teflon (registered trademark) filterhaving an opening size of 0.2 μm.

This composition was then applied to a silicon substrate having a 200nm-thick platinum coating film to a thickness of 100 nm by spin coatingat 2,000 rpm at an ambient humidity of 9 g/m³ and then the solvent wasevaporated at 145° C. The thickness of the film after the removal of thesolvent was 63 nm.

Thereafter, when the film was heated at 400° C. in the air for 30minutes, a transparent film was obtained on the substrate. The thicknessof this film was 40 nm. The same procedure was repeated twice to formthree coating layers in order to obtain a laminated film. The totalthickness of this laminated film was 110 nm. When the ESCA spectrum ofthis film was measured, this film was found to be a tantalum oxide film.The leak current of the obtained film was 10⁻⁸ A/cm² which wassatisfactory as an insulating film for semiconductor devices.

Example 11

A composition for forming a tantalum oxide film was prepared bydissolving 1.0 g of the product obtained in Synthetic Example 7 and 0.9g of methyl orthoformate in 8.1 g of propylene glycol monopropyl ether(isomer mixture) and filtering the resulting solution with a Teflon(registered trademark) filter having an opening size of 0.2 μm.

This composition was then applied to a silicon substrate having a 200nm-thick platinum coating film to a thickness of 100 nm by spin coatingat 2,000 rpm at an ambient humidity of 7 g/m³ and then the solvent wasevaporated at 145° C. The thickness of the film after the removal of thesolvent was 60 nm.

Thereafter, when the film was exposed to light having a wavelength of254 nm at an exposure amount of 50,000 J/m² in an oxygen atmosphere andthen heated at 400° C. in the air for 30 minutes, a transparent film wasobtained on the substrate. The thickness of this film was 35 nm. Whenthe ESCA spectrum of this film was measured, this film was found to be atantalum oxide film. The leak current of the obtained film was 10⁻⁸A/cm² which was satisfactory as an insulating film for semiconductordevices.

Example 12

A transparent film was obtained in the same manner as in Example 9except that 1.0 g of the product obtained in Synthetic Example 8 and 0.9g of ethyl orthoformate were dissolved in 8.1 g of diethylene glycol.The thickness of this film was 42 nm. When the ESCA spectrum of thisfilm was measured, the film was found to be a tantalum oxide film. Theleak current of the obtained film was 10⁻⁸ A/cm² which was satisfactoryas an insulating film for semiconductor devices.

Example 13

A transparent film was obtained in the same manner as in Example 9except that 1.0 g of the product obtained in Synthetic Example 9 and 0.9g of methyl orthobenzoate were dissolved in 8.1 g of butanol. Thethickness of this film was 31 nm. When the ESCA spectrum of this filmwas measured, the film was found to be a tantalum oxide film. The leakcurrent of the obtained film was 10⁻⁸ A/cm² which was satisfactory as aninsulating film for semiconductor devices.

Example 14

A composition for forming a tantalum oxide film was prepared bydissolving 1.0 g of the white solid obtained in Synthetic Example 10 in9 g of propylene glycol monomethyl ether (isomer mixture) and filteringthe resulting solution with a Teflon (registered trademark) filterhaving an opening size of 0.2 μm.

This composition was then applied to a silicon substrate having a 0.2μm-thick platinum coating film by spin coating at 2,000 rpm at anambient humidity of 3 g/m³ in the air and then the solvent wasevaporated on a hot plate heated at 145° C. at an ambient humidity of 3g/m³. The thickness of the film after the removal of the solvent was0.050 μm. Thereafter, when the film was heated at 400° C. in the air for30 minutes, a transparent film was obtained on the substrate. Thethickness of this film was 0.030 μm. When the ESCA spectrum of this filmwas measured, a peak derived from the Ta_(4f7/2) orbit was observed at26 eV and a peak derived from the O_(1s) orbit was observed at 531 eV,which proved that this film was a tantalum oxide film. This ESCAspectrum is shown in FIG. 8. After a platinum film was formed on thisfilm to a thickness of 0.060 μm by sputtering, the leak current at afield strength of 1.5 V/cm⁻¹ was 10⁻⁸ A/cm² which was satisfactory as aninsulating film for semiconductor devices.

Example 15

A composition for forming a tantalum oxide film was prepared bydissolving 1.0 g of the white solid obtained in Synthetic Example 10 in9 g of propylene glycol monomethyl ether (isomer mixture) and filteringthe resulting solution with a Teflon (registered trademark) filterhaving an opening size of 0.2 μm.

This composition was then applied to a silicon substrate having a 0.2μm-thick platinum coating film by spin coating at 2,000 rpm at anambient humidity of 3 g/m³ and then the solvent was evaporated on a hotplate heated at 145° C. at an ambient humidity of 3 g/m³ in the air. Thethickness of the film after the removal of the solvent was 0.048 μm.Thereafter, when the film was exposed to light having a wavelength of254 nm at an exposure amount of 5 J/cm² in an oxygen atmosphere and thenheated at 400° C. in the air for 30 minutes, a transparent film wasobtained on the substrate. The thickness of this film was 0.027 μm. Whenthe ESCA spectrum of this film was measured, this film was found to be atantalum oxide film. After a platinum film was formed on this film to athickness of 0.060 μm by sputtering, the leak current at a fieldstrength of 1.5 V/cm⁻¹ was 10⁻⁹ A/cm² which was satisfactory as aninsulating film for semiconductor devices.

Example 16

A composition for forming a tantalum oxide film was prepared bydissolving 1 g of the white solid obtained in Synthetic Example 6 in 9 gof propylene glycol monomethyl ether (isomer mixture) and filtering theresulting solution with a Teflon (registered trademark) filter having anopening size of 0.2 μm.

This composition was then applied to a silicon substrate having a 0.2μm-thick platinum coating film to a thickness of 0.090 μm by spincoating at 2,000 rpm at an ambient humidity of 3 g/m³. Thereafter, whenthe film was exposed to light having a wavelength of 254 nm at anexposure amount of 5 J/cm² in an oxygen atmosphere and then heated at400° C. in the air for 30 minutes, a transparent film was obtained onthe substrate. The thickness of this film was 0.027 μm. When the ESCAspectrum of this film was measured, the film was found to be a tantalumoxide film. After a platinum film was formed on this film to a thicknessof 0.060 μm by sputtering, the leak current at a field strength of 1.5V/cm⁻¹ was 10⁻⁹ A/cm² which was satisfactory as an insulating film forsemiconductor devices.

Example 17

A composition for forming a tantalum oxide film was prepared bydissolving 1 g of the white solid obtained in Synthetic Example 10 in 9g of propylene glycol monomethyl ether and filtering the resultingsolution with a Teflon (registered trademark) filter having an openingsize of 0.2 μm.

This composition was then applied to a silicon substrate having a 0.2μm-thick platinum coating film by spin coating at 2,000 rpm at anambient humidity of 3 g/m³ and then the solvent was evaporated on a hotplate heated at 145° C. at an ambient humidity of 3 g/m³ in the air. Thethickness of the film after the removal of the solvent was 0.052 μm.

Thereafter, when the film was heated at 400° C. in the air for 30minutes, a transparent film was obtained on the substrate. The thicknessof this film was 0.030 μm. Further, a film was formed on this film byspin coating at 2,000 rpm at an ambient humidity of 5 g/m³, the solventwas evaporated on a hot plate heated at 145° C. and the film was heatedat 400° C. in the presence of air for 30 minutes to obtain a laminatedfilm. The total thickness of this laminated film was 0.070 μm. When theESCA spectrum of this film was measured, the film was found to be atantalum oxide film. After a platinum film was formed on this film to athickness of 0.060 μm by sputtering, the leak current at a fieldstrength of 1.5 V/cm⁻¹ was 10⁻⁹ A/cm² which was satisfactory as aninsulating film for semiconductor devices.

Example 18

A composition for forming a tantalum oxide film was prepared bydissolving 1 g of the white solid obtained in Synthetic Example 10 in 9g of propylene glycol monomethyl ether (isomer mixture) and filteringthe resulting solution with a Teflon (registered trademark) filterhaving an opening size of 0.2 μm. This composition was then applied to asilicon substrate having a 0.2 μm-thick platinum coating film by spincoating at 2,000 rpm at an ambient humidity of 1 g/m³ and then thesolvent was evaporated on a hot plate heated at 145° C. at an ambienthumidity of 1 g/m³ in the air. The thickness of the film after theremoval of the solvent was 0.048 μm.

Thereafter, when the film was heated at 400° C. in the air for 30minutes, a transparent film was obtained on the substrate. The thicknessof this film was 0.035 μm. When the ESCA spectrum of this film wasmeasured, the film was found to be a tantalum oxide film. The leakcurrent of the obtained film was 10⁻⁹ A/cm² which was satisfactory as aninsulating film for semiconductor devices.

Example 19

A composition for forming a tantalum oxide film was prepared bydissolving 1 g of the white solid obtained in Synthetic Example 11 in 9g of propylene glycol monomethyl ether (isomer mixture) and filteringthe resulting solution with a Teflon (registered trademark) filterhaving an opening size of 0.2 μm.

This composition was then applied to a silicon substrate having a 0.2μm-thick platinum coating film by spin coating at 2,000 rpm at anambient humidity of 3 g/m³ and then the solvent was evaporated on a hotplate heated at 145° C. at an ambient humidity of 3 g/m³ in the air. Thethickness of the film after the removal of the solvent was 0.051 μm.

Thereafter, when the film was heated at 400° C. in the air for 30minutes, a transparent film was obtained on the substrate. The thicknessof this film was 0.030 μm. When the ESCA spectrum of this film wasmeasured, the film was found to be a tantalum oxide film. After a 0.060μm-thick platinum film was formed on this film by sputtering, the leakcurrent at a field strength of 1.5 V/cm⁻¹ was 10⁻⁵ A/cm² which provedthat the film could be used as an insulating film for semiconductordevices.

What is claimed is:
 1. A composition for forming a tantalum oxide film, consisting essentially of at least one tantalum-containing product selected from the group consisting of (A1) a reaction product of (a1) a tantalum alkoxide and (a2) at least one compound selected from the group consisting of an amino alcohol having no more than one hydroxyl group, a compound having two or more hydroxyl groups in the molecule, a β-diketone, a β-ketoester, an ester of β-dicarboxylic acid, lactic acid, ethyl lactate and 1,5-cyclooctadiene, and (A2) a hydrolyzate of the reaction product.
 2. The composition of claim 1, wherein the tantalum alkoxide (a1) is represented by the following formula (1): Ta(OR)₅  (1) wherein R is an alkyl group having 1 to 6 carbon atoms and may be the same or different.
 3. The composition of claim 1, wherein the tantalum-containing product is a reaction product of the component (a1) and the component (a2).
 4. The composition of claim 1, wherein the reaction conversion of the alkoxyl groups of the component (a1) in the reaction product of the component (a1) and the component (a2) is 50 mol % or more.
 5. The composition of claim 1, wherein the number average molecular weight of the reaction product of the component (a1) and the component (a2) is 300 to 10,000.
 6. The composition of claim 1, wherein the component (a2) is a compound having two or more hydroxyl groups in the molecule.
 7. The composition of claim 1 which further comprises (B) an ester of orthocarboxylic acid.
 8. A process for forming a tantalum oxide film, comprising applying the composition of claim 1 to a substrate and subjecting it to at least one of a heat treatment and a photo-treatment to form a tantalum oxide film.
 9. The process of claim 8, wherein the application is carried out at an ambient humidity of 0.5 g/m³ or less.
 10. A tantalum oxide film formed by the process of claim
 8. 11. An insulating film for semiconductor devices which is the tantalum oxide film of claim
 10. 12. The composition of claim 2, wherein the component (a2) is a compound having two or more hydroxyl groups in the molecule.
 13. The composition of claim 3, wherein the component (a2) is a compound having two or more hydroxyl groups in the molecule.
 14. The composition of claim 4, wherein the component (a2) is a compound having two or more hydroxyl groups in the molecule.
 15. The composition of claim 5, wherein the component (a2) is a compound having two or more hydroxyl groups in the molecule.
 16. A composition comprising at least one tantalum-containing compound selected from the group consisting of (A1) a reaction product of (a1) a tantalum alkoxide and (a2) at least one compound selected from the group consisting of an amino alcohol having no more than one hydroxyl group, a compound having two or more hydroxyl groups in the molecule, a β-diketone, a β-ketoester, an ester of β-dicarboxylic acid, lactic acid, ethyl lactate and 1,5-cyclooctadiene, (A2) a hydrolyzate of the reaction product of (a1) and (a2); and (B) an ester of an orthocarboxylic acid.
 17. The composition of claim 16, wherein the tantalum alkoxide (a1) is represented by formula (1): Ta(OR)₅  (1) wherein R is an alkyl group having 1 to 6 carbon atoms and may be the same or different.
 18. The composition of claim 16, wherein the reaction product of (a1) and (a2) has a conversion of the alkoxyl groups of the component (a1) in the reaction product of the component (a1) and the component (a2) of 50 mol % or more.
 19. The composition of claim 16, wherein the number average molecular weight of the reaction product of the component (a1) and (a2) is 300 to 10,000.
 20. The composition of claim 16, wherein the component (a2) is a compound having two or more hydroxyl groups in the molecule.
 21. A process for forming a tantalum oxide film, comprising applying the composition of claim 16 to a substrate, and subjecting the substrate to at least one of a heat treatment and a photo-treatment to form a tantalum oxide film.
 22. The process of claim 21, wherein applying is carried out at an ambient humidity of 0.5 g/m³ or less.
 23. A tantalum oxide film formed by the process of claim
 21. 24. An insulating film for semiconductor devices which is the tantalum oxide film of claim
 23. 25. The composition as claimed in claim 16, wherein the ester of the orthocarboxylic acid (B) is selected from the group consisting of trimethylorthoformate, triethylorthoformate, trimethylorthobenzoate and mixtures thereof.
 26. The composition as claimed in claim 16, wherein the ester of the orthocarboxylic acid (B) is present in an amount of 0.05 to 50 wt. %.
 27. The composition as claimed in claim 16, wherein the ester of the orthocarboxylic acid (B) is present in an amount of from 0.5 to 20 wt. %.
 28. The process as claimed in claim 8, wherein the tantalum oxide film has a leak current of from 10⁻⁸ A/cm² to 10⁻⁹ A/cm².
 29. The process as claimed in claim 21, wherein the tantalum oxide film has a leak current of from 10⁻⁸ A/cm² to 110⁻⁹ A/cm². 